Category learning is learning to classify stimuli into different groups, or categories. Corticostriatal networks connecting the striatum, including the caudate and putamen, with the cerebral cortex play an important role in category learning. The overall aim of this project is to differentiate between the functions that three of these networks, one linking the head of the caudate with frontal cortex, and one linking the body/tail of the caudate to visual cortex, and one linking the putamen with sensorimotor cortex, serve in classification learning using functional Magnetic Resonance Imaging (fMRI). Previous studies have linked the head of the caudate to processing feedback (i.e., being told that a classification response is correct or incorrect). The body and tail of the caudate, along with the putamen, has been linked to learning and executing associations between stimuli and categories. The first aim is to investigate the sensitivity of the head of the caudate to both verbal feedback and monetary reward, and compare how positive and negative associations with stimuli are represented. The second aim is to investigate how the body and tail of the caudate interacts with visual cortex during learning. The third aim is to distinguish between the roles of the body and tail of the caudate and putamen in categorization. The fourth aim is to separate the contributions of the striatum to categorization from those of the medial temporal lobe. The striatum is affected in many disorders, including Parkinson's disease, Huntington's disease, schizophrenia, and Tourette syndrome. Behavioral studies have shown that category learning is impaired in all of these disorders. The proposed studies may provide insight into the types of learning problems seen in patients with these diseases.